I'm wondering if asking your pdoc if you can lower the Seroquel dose might help. 300 mg is a 'therapeutic' dose (to help with BP) not just a sleep dose. I've (and I'm sure others) have taken far lower doses when it's just for sleep (I've taken 25mg and it's knocked me out). Now, if s/he is prescribing it for BP as well as sleep, then maybe it's an appropriate dose. But please ask your pdoc before changing anything.

I agree with another poster that you sound very depressed. Maybe medication for this might help, maybe therapy, maybe both. Are you in therapy?